1. Field of the Invention
This invention relates to an apparatus for treating water, comprising a membrane filter, which at its inlet end is adapted to be connected by a prefiltering filter to a water supply line and serves to treat water by reverse osmosis and at its outlet end is connected to a waste water line and a pure water line, which opens into a drinking water tank, which is constituted by a diaphragmless container, which is connected to air supply means for supplying compressed air to said tank and from which a rising line extends to a dispenser for drinking water.
2. Description of the Prior Art
Owing to the progressively increasing pollution of the groundwater, many waterworks can no longer supply water having the quality of true drinking water and it is hardly possible still to comply with legally prescribed limits for the contents of pollutants in the water. As a result, water from the main may adversely affect the health. Apparatuses for treating water are mounted in most cases under a washbasin and are intended to purify tap water in order to prepare healthy drinking water. Membrane filters for a reverse osmosis have proved most satisfactory for that purpose. Reverse osmosis is a naturally performed method of treating water without heating or chemically changing the water. In that method, water under line pressure is forced against a semipermeable membrane, which has microscopically small pores, by which the water molecules are separated from the pollutant molecules. This is due to the fact that the water molecules can penetrate through the membrane whereas the larger pollutant molecules are rejected by the pores and are enriched in the waste water. As a result, the permeate delivered by the membrane filter is pure and healthy water and the waste water is discharged as a pollutant concentrate through the waste water line. Most of the known water-treating apparatuses of that kind comprise a drinking water tank, which constitutes a pressure accumulator, which contains a rubber diaphragm to provide the water pressure that is required for a tapping of drinking water. But that rubber diaphragm deteriorates the taste of the water and for this reason the tank must be succeeded by an active carbon filter, which adds to the cost of the apparatus. Besides, bacteria may accumulate on the rubber diaphragm and also in the active carbon filter and will inevitably introduce germs into the water. That risk is further increased by the fact that the pressure accumulator is permanently sealed at its top so that it is virtually impossible to clean the interior of the drinking water tank and the rubber diaphragm and an accumulation of bacteria cannot be prevented in the long run. A further disadvantage of the known diaphragm pressure accumulators resides in that they apply to the membrane filter a considerable backpressure by which the rejection of pollutants in the reverse osmosis is adversely affected.
U.S. Pat. No. 4,502,953 discloses a water-treating apparatus in which the drinking water tank does not contain a diaphragm and a tapping of water is permitted by means for supplying compressed air to said tank and a rising line. For that purpose a cushion of compressed air introduced through an inlet valve is permanently maintained above the water level in the tank and is utilized to force water through the rising line to the drinking water dispenser as required. In that case a special control valve is required to prevent an escape of the compressed air as the tank is being exhausted. This requirement may give rise to malfunction. Besides, the pressure conditions change in dependence on the level of the water in the tank and on temperature so that the tapping conditions are not uniform. The tank must consist of a pressure container, and the high backpressure also adversely affects the reverse osmosis.